The Forbidden Cities are what the Elves call human territory. All of the world we know is part of the Forbidden Cities.
Forbidden Cities Visited in The Keeper of the Lost Cities Edit
San Diego, California Edit
Paris, France Edit
Mt. Everest Edit
Florence, Italy Edit
-Visited by Sophie, Fitz, Keefe, Dex, Biana, Della, Mr. Forkle, possibly other members of the Black Swan, and at least one Pyrokinetic in the Neverseen, so possibly Brant or Fintan. Most likely Brant, as Fintan usually stays where it's safe.